共查询到20条相似文献,搜索用时 31 毫秒
1.
Craig J. Kennedy Graeme J. Cameron Adriana Šturcová David C. Apperley Clemens Altaner Timothy J. Wess Michael C. Jarvis 《Cellulose (London, England)》2007,14(3):235-246
Cellulose isolated from celery collenchyma is typical of the low-crystallinity celluloses that can be isolated from primary
cell-walls of higher plants, except that it is oriented with high uniformity. The diameter of the microfibrils of celery collenchyma
cellulose was estimated by three separate approaches: 13C NMR measurement of the ratio of surface to interior chains; estimation of the dimensions of the crystalline lattice from
wide angle X-ray scattering (WAXS) measurements using the Scherrer equation; and the observation that microfibrils of this
form of cellulose have the unusual property of packing into an irregular array from which small angle X-ray scattering (SAXS)
shows features of both form and interference functions. The interference function contributing to the SAXS pattern implied
a mean microfibril centre-to-centre distance of 3.6 nm, providing an upper limit for the diameter. However modelling of the
scattering pattern from an irregular array of microfibrils showed that the observed scattering curve could be matched at a
range of diameters down to 2.4 nm, with the intervening space more or less sparsely occupied by hemicellulose chains. The
lateral extent of the crystalline lattice normal to the 200 plane was estimated as a minimum of 2.4 nm by WAXS through the
Scherrer equation, and a diameter of 2.6 nm was implied by the surface: volume ratio determined by 13C NMR. The WAXS and NMR measurements both depended on the assumption that the surface chains were positioned within an extension
of the crystalline lattice. The reliability of this assumption is uncertain. If the surface chains deviated from the lattice,
both the WAXS and the NMR data would imply larger microfibril diameters within the range consistent with the SAXS pattern.
The evidence presented is therefore all consistent with microfibril diameters from about 2.4 to 3.6 nm, larger than has previously
been suggested for primary-wall cellulose. Some degree of aggregation may have occurred during the isolation of the cellulose,
but the larger microfibril diameters within the range proposed are a consequence of the novel interpretation of the experimental
data from WAXS and NMR and are consistent with previously published data if these are similarly interpreted. 相似文献
2.
This study examined the relationship between the functions of plant cells and the characteristics of cellulose microfibril
aggregates in the cell walls. For this purpose, the mature bamboo (Phyllostachys pubescens) culm was separated into fiber and parenchyma cells, and then the morphological and physical properties of the cellulose
microfibril aggregates isolated from both cells were compared. SEM observations revealed that both fiber and parenchyma cells
consist of similar microfibril aggregates approximately 15–20 nm in width. Moreover, X-ray analysis and the tensile tests
of the sheets prepared from the microfibril aggregates showed that the cellulose microfibrils isolated from fiber and parenchyma
cells had almost the same cellulose crystallinity and longitudinal Young’s modulus in the dry state. These results suggest
that all the cellulose microfibrils synthesized in the same individual exhibit the same characteristics in the dry state regardless
of cell function. 相似文献
3.
Paavo A. Penttilä Petri Kilpeläinen Lasse Tolonen Jussi-Petteri Suuronen Herbert Sixta Stefan Willför Ritva Serimaa 《Cellulose (London, England)》2013,20(5):2335-2347
Pressurized hot water extraction with a flow-through system was used to extract hemicelluloses and lignin from birch sawdust. The structure of the extraction residue was studied on various levels. Molecular mass distributions were determined with gel permeation chromatography and the crystal structure of cellulose was characterized using wide-angle X-ray scattering (WAXS). Information on the short-range order of cellulose microfibrils and on the nanoscale pore structure was obtained with small-angle X-ray scattering (SAXS), and the micrometre scale cellular morphology was imaged with X-ray microtomography. The pressurized hot water treatment was observed to increase the lateral width of cellulose crystallites, determined with WAXS, whereas a possible small decrease in the crystallinity of cellulose compared to native wood was detected. The molecular mass of cellulose remained at a relatively high level. According to the SAXS results, a tighter lateral association of cellulose microfibrils was observed in the extracted samples, which possibly led to opening of pores between bundles of microfibrils, as indicated by an increased specific surface area. A reduction in the thickness of the fibre cell walls was evidenced by X-ray microtomography. 相似文献
4.
Kabindra Kafle Xiaoning Xi Christopher M. Lee Bernhard R. Tittmann Daniel J. Cosgrove Yong Bum Park Seong H. Kim 《Cellulose (London, England)》2014,21(2):1075-1086
Cellulose microfibril orientation in plant cell walls changes during cell expansion and development. The cellulose microfibril orientation in the abaxial epidermis of onion scales was studied by atomic force microscopy (AFM) and sum frequency generation (SFG) vibrational spectroscopy. Onion epidermal cells in all scales are elongated along the onion bulb axis. AFM images showed that cellulose microfibrils exposed at the innermost surface of the abaxial epidermis are oriented perpendicular to the bulb axis in the outer scales and more dispersed in the inner scales of onion bulb. SFG analyses can determine the orientation of cellulose microfibrils averaged over the entire thickness of the cell wall. We found that the average orientation of cellulose microfibrils inside onion abaxial epidermal cell walls as revealed by SFG is similar to the orientation observed at the innermost cell wall surface by AFM. The capability to determine the average orientation of cellulose microfibrils in intact cell walls will be useful to study how cellulose microfibril orientation is related to biomechanical properties and the growth mechanism of plant cell walls. 相似文献
5.
Tian Zhang Sahar Mahgsoudy-Louyeh Bernhard Tittmann Daniel J. Cosgrove 《Cellulose (London, England)》2014,21(2):853-862
For more than 10 years epidermal cell layers from onion scales have been used as a model system to study the relationship between cellulose orientation, cell growth and tissue mechanics. To bring such analyses to the nanoscale, we have developed a procedure for preparing epidermal peels of onion scales for atomic force microscopy to visualize the inner surface (closest to the plasma membrane) of the outer epidermal wall, with minimal disturbance and under conditions very close to the native state of the cell wall. The oriented, multilayer distribution of cellulose microfibrils, approximately ~3 nm wide, is readily observed over extended lengths, along with other features such as the distribution of matrix substances between and on top of microfibrils. The microfibril orientation and alignment appear more dispersed in younger scales compared with older scales, consistent with reported values for mechanical and growth anisotropy of whole epidermal sheets. These results open the door to future work to relate cell wall structure at the nm scale with larger-scale tissue properties such as growth and mechanical behaviors and the action of cell wall loosening agents to induce creep of primary cell walls. 相似文献
6.
Lynne H. Thomas V. Trevor Forsyth Anne Martel Isabelle Grillo Clemens M. Altaner Michael C. Jarvis 《Cellulose (London, England)》2014,21(6):3887-3895
The structure of cellulose microfibrils in situ in wood from the dicotyledonous (hardwood) species cherry and birch, and the vascular tissue from sunflower stems, was examined by wide-angle X-ray and neutron scattering (WAXS and WANS) and small-angle neutron scattering (SANS). Deuteration of accessible cellulose chains followed by WANS showed that these chains were packed at similar spacings to crystalline cellulose, consistent with their inclusion in the microfibril dimensions and with a location at the surface of the microfibrils. Using the Scherrer equation and correcting for considerable lateral disorder, the microfibril dimensions of cherry, birch and sunflower microfibrils perpendicular to the [200] crystal plane were estimated as 3.0, 3.4 and 3.3 nm respectively. The lateral dimensions in other directions were more difficult to correct for disorder but appeared to be 3 nm or less. However for cherry and sunflower, the microfibril spacing estimated by SANS was about 4 nm and was insensitive to the presence of moisture. If the microfibril width was 3 nm as estimated by WAXS, the SANS spacing suggests that a non-cellulosic polymer segment might in places separate the aggregated cellulose microfibrils. 相似文献
7.
Kabindra Kafle Rui Shi Christopher M. Lee Ashutosh Mittal Yong Bum Park Ying-Hsuan Sun Sunkyu Park Vincent Chiang Seong H. Kim 《Cellulose (London, England)》2014,21(4):2219-2231
The cellulose microfibril assemblies in secondary cell walls of tension wood and compression wood were studied with vibrational sum frequency generation (SFG) spectroscopy. The tension wood contains the gelatinous layer with highly-crystalline and highly-aligned cellulose microfibrils. The SFG spectral features of tension wood changed depending on the azimuth angle between the polarization of the incident IR beam and the preferential alignment axis of the cellulose microfibrils. The SFG spectra of the compression wood did not show any dependence on the azimuth angle, implying that the overall orientation of cellulose microfibrils in compression wood is not highly aligned. Instead, the decrease of cellulose content in compression wood brought about larger separation between cellulose microfibrils, which was manifested as changes in CH2/OH intensity ratio in SFG spectra. These results implied that SFG spectral features are sensitive to cellulose microfibril alignments and inter-fibrillar separations. 相似文献
8.
Juan Guo Harald Rennhofer Yafang Yin Helga C. Lichtenegger 《Cellulose (London, England)》2016,23(4):2325-2340
Tracking the changes of cellulose crystallites upon thermo-hygro-mechanical treatment is essential to understand the response of wood cell walls to steam and compression. In this paper the influence of Compression combined with Steam (CS) treatment on wood cellulose crystallites and pores structure of Chinese fir (Cunninghamia lanceolata) was studied under different steaming temperatures and compression ratios. Small-angle X-ray scattering and wide-angle X-ray scattering were used to investigate the changes of cellulose crystallites dimension, aspect ratio, fibril diameter distribution, non-crystalline fraction, the number of chains in each microfibril, as well as the fractal dimension and size of pores in response to CS treatment conditions. Results indicate that the crystallinity increased due to CS treatment, but did not show alteration with varying CS treatment conditions, i.e. seemed nearly unaffected by higher temperatures or compression ratio, both for earlywood and latewood. The cellulose crystallite diameter depended on processing parameters: it increased with increasing treatment temperature. No considerable differences were found for earlywood and latewood. We interpret our findings as a rearrangement of adjacent cellulose chains towards higher crystalline perfection attributing to the increase in crystallinity. The same effect allows a larger coherence length of crystalline order and therefore features an increasing cross-sectional dimension. In general we can state that the CS treatment leads to higher crystallinity and more perfectly arranged cellulose crystals, while it does not greatly affect the microfibril diameter but rather the amorphous regions of the microfibrils and the surrounding hemicellulose and lignin. 相似文献
9.
The focus of this study has been to isolate cellulose microfibril aggregates by the one-time grinding treatment from wood, rice straw and potato tuber, and to compare their morphological and mechanical properties. Field emission scanning electron microscopy images showed that the diameter range of isolated microfibril aggregates from wood, 12–20 nm, was smaller than those from rice straw and potato tuber, 12–35 nm and 12–55 nm, respectively. These differences were observed even in the purified rice straws and potato tuber before the grinder treatment, but were hardly observed in the purified wood. The results of X-ray analysis and tensile tests indicated that there were no significant differences among the sources in the cellulose crystallinity and Young’s modulus of the isolated microfibril aggregates in the dry state. These results suggest that the inherent characteristics of cellulose microfibril aggregates in the dry state are very similar regardless of plant sources and tissue functions. 相似文献
10.
Stained and unstained sections of nylon 6 fibers are examined by means of transmission electron microscopy. Data are presented regarding dimensions and shape of macrofibrils, microfibrils, amorphous, and crystalline domains of the microfibril and the spacing between the microfibrils. The new results support the conclusions of a previous SAXS and diffusion study carried out with the same fibers. 相似文献
11.
Minoru Kimura Zi-Dong Qi Hayaka Fukuzumi Shigenori Kuga Akira Isogai 《Cellulose (London, England)》2014,21(5):3193-3201
Nitrogen adsorption was used to characterize mesoporous structures in never-dried softwood cellulose fibers. Distinct inflections in desorption isotherms were observed over the relative vapor pressure (P/P0) range of 0.5–0.42 for never-dried cellulose fibers and partially delignified softwood powders. The reduction in N2 adsorption volume was attributed to cavitation of condensed N2 present in mesopores formed via lignin removal from wood cell walls during delignification. The specific surface areas of significantly delignified softwood powders were ~150 m2 g?1, indicating that in wood cell walls 16 individual cellulose microfibrils, each 3–4 nm in width, form one cellulose fibril bundle surrounded with a thin layer of lignin and hemicelluloses. Analysis of N2 adsorption isotherms indicates that mesopores in the softwood cellulose fibers and partially delignified softwood powders had peaks ranging from 4 to 20 nm in diameter. 相似文献
12.
H. S. Barud R. M. N. Assunção M. A. U. Martines J. Dexpert-Ghys R. F. C. Marques Y. Messaddeq S. J. L. Ribeiro 《Journal of Sol-Gel Science and Technology》2008,46(3):363-367
Bacterial cellulose (BC) hydrated membranes present nanometric reticulated structure that can be used as a template in the
preparation of new organic–inorganic hybrids. BC–silica hybrids were prepared from BC membranes and tetraethoxysilane, (TEOS)
at neutral pH conditions at room temperature. Macroscopically homogeneous membranes were obtained containing up to 66 wt.%
of silica spheres, 20–30 nm diameter. Scanning electron micrographs clearly show the silica spheres attached to cellulose
microfibrils. By removing the cellulose, the silica spheres can be easily recovered. The new hybrids are stable up to 300 °C
and display a broad emission band under UV excitation assigned to oxygen-related defects at the silica particles surface.
Emission color can be tuned by changing the excitation wavelength. 相似文献
13.
Structure of cellulose and microcrystalline cellulose from various wood species, cotton and flax studied by X-ray scattering 总被引:2,自引:1,他引:1
Kirsi Leppänen Seppo Andersson Mika Torkkeli Matti Knaapila Nina Kotelnikova Ritva Serimaa 《Cellulose (London, England)》2009,16(6):999-1015
The structure of microcrystalline cellulose (MCC) made by mild acid hydrolysis from cotton linter, flax fibres and sulphite
or kraft cooked wood pulp was studied and compared with the structure of the starting materials. Crystallinities and the length
and the width of the cellulose crystallites were determined by wide-angle X-ray scattering and the packing and the cross-sectional
shape of the microfibrils were determined by small-angle X-ray scattering. The morphological differences were studied by scanning
electron microscopy. A model for the changes in microfibrillar structure between native materials, pulp and MCC samples was
proposed. The results indicated that from softwood or hardwood pulp, flax cellulose and cotton linter MCC with very similar
nanostructures were obtained with small changes in reaction conditions. The crystallinity of MCC samples was 54–65%. The width
and the length of the cellulose crystallites increased when MCC was made. For example, between cotton and cotton MCC the width
increased from 7.1 nm to 8.8 nm and the length increased from 17.7 nm to 30.4 nm. However, the longest crystallites were found
in native spruce wood (35–36 nm). 相似文献
14.
AFM observation of ultrathin microfibrils in fruit tissues 总被引:1,自引:0,他引:1
Hiroshi Niimura Tomoya Yokoyama Satoshi Kimura Yuji Matsumoto Shigenori Kuga 《Cellulose (London, England)》2010,17(1):13-18
Polysaccharide microfibrils in fruit tissue of higher plants (strawberry, peach, and rambutan) were examined by atomic force
microscopy (AFM). For preserving native cellulose microfibrils, a combination of 2% NaClO2 and 4% NaOH extraction was applied to the materials. This corresponds to mild alkali extractin of holocellulose, and denoted
here as weak alkali-resistant polysaccharide, WARP. The amount of neutral sugars corresponded to 53–95% of that of WARP. Glucose
was the most abundant in the neutral sugars, being 74–87%. AFM examination of microfibrils dispersed on mica substrate allowed
accurate determination of fibril widths as 1.0–2.0 nm. Their straight fibrillar shape and the results of X-ray diffraction
and infrared spectroscopy indicate that these fibrils are cellulose. These results constitute direct evidence for existence
of ultrafine cellulose microfibrils hitherto assumed from X-ray diffraction and NMR analyses. 相似文献
15.
Zitting Aleksi Paajanen Antti Rautkari Lauri Penttilä Paavo A. 《Cellulose (London, England)》2021,28(17):10765-10776
Cellulose - Structural changes of cellulose microfibrils and microfibril bundles in unmodified spruce cell wall due to drying in air were investigated using time-resolved small-angle neutron... 相似文献
16.
Thünemann AF Klobes P Wieland C Bruzzano S 《Analytical and bioanalytical chemistry》2011,401(4):1101-1108
The analysis of the porosity of materials is an important and challenging field in analytical chemistry. The gas adsorption
and mercury intrusion methods are the most established techniques for quantification of specific surface areas, but unfortunately,
dry materials are mandatory for their applicability. All porous materials that contain water and other solvents in their functional
state must be dried before analysis. In this process, care has to be taken since the removal of solvent bears the risk of
an incalculable alteration of the pore structure, especially for soft materials. In the present paper, we report on the use
of small-angle X-ray scattering (SAXS) as an alternative analysis method for the investigation of the micro and mesopores
within cellulose beads in their native, i.e., water-swollen state; in this context, they represent a typical soft material.
We show that even gentle removal of the bound water reduces the specific surface area dramatically from 161 to 109 m2 g−1 in cellulose bead sample type MT50 and from 417 to 220 m2 g−1 in MT100. Simulation of the SAXS curves with a bimodal pore size distribution model reveals that the smallest pores with
radii up to 10 nm are greatly affected by drying, whereas pores with sizes in the range of 10 to 70 nm are barely affected.
The SAXS results were compared with Brunauer–Emmett–Teller results from nitrogen sorption measurements and with mercury intrusion
experiments. 相似文献
17.
SHAUNE J. HANLEY JEAN-FRANCOIS REVOL LOUIS GODBOUT DEREK G. GRAY 《Cellulose (London, England)》1997,4(3):209-220
Atomic force microscopy (AFM), tapping mode atomic force microscopy (TM-AFM) and transmission electron microscopy (TEM) have
been used to image the cell wall, ultrathin sections of whole cells and cellulose microfibrils prepared from the green alga
Micrasterias denticulata. Measurements of the microfibril dimensions are in agreement with earlier observations carried out by electron microscopy.
Images at the molecular level of the surface of the microfibrils were obtained with AFM and show regular periodicities along
the microfibril axis that correspond to the fibre and glucose repeat distances of cellulose. Twisted regions visible at intervals
along the microfibrils dried down onto substrates were noted to be right-handed in over 100 observations by TEM, AFM and TM-AFM.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
18.
In this article, a new method based on a generalized method of cells and laminate analogy approach was used to predict the elastic properties of natural fibers. The elastic properties of cellulose crystals and amorphous cellulose were adopted to calculate the effective properties of microfibrils. A ten-layer antisymmetrical laminated structure was used to predict the effective properties of cell walls. The effects of the aspect ratio and volume fraction of cellulose crystal, the microfibril angle in the S2 layer and the lumen ratio of fiber on the axial Young’s moduli of natural fibers were analyzed in detail. The results show that the predicted properties of fibers are those of the cell fibers, and the final elastic properties of natural fibers can be obtained with the volume fractions of cell fibers as the corresponding conversion coefficients. The multiscale method is very effective in the predictions of the axial Young’s moduli of natural fibers. 相似文献
19.
Yan Li Guozhu Li Yunling Zou Qingjun Zhou Xiaoxue Lian 《Cellulose (London, England)》2014,21(1):301-309
Cellulose nanofibers with a diameter of 70 nm and lengths of approximately 400 nm were fabricated from partly mercerized cotton fibers by acid hydrolysis. Morphological evolution of the hydrolyzed cotton fibers was investigated by powder X-ray diffraction, Fourier transform infrared analysis and field emission scanning electron microscopy. The XRD results show that the cellulose I was partially transformed into cellulose II by treatment with 15 % NaOH at 150° for 3 h. The crystallinity of this partially mercerized sample was lower than the samples that were converted completely to cellulose II by higher concentrations of NaOH. The intensities of all of the diffraction peaks were noticeably increased with increased hydrolysis time. Fourier transform infrared results revealed that the chemical composition of the remaining nanofibers of cellulose I and II had no observable change after acidic hydrolysis, and there was no difference between the hydrolysis rates for cellulose I or II. The formation of cellulose nanofibers involves three stages: net-like microfibril formation, then short microfibrils and finally nanofibers. 相似文献
20.
Paula Eronen Monika Österberg Anna-Stiina Jääskeläinen 《Cellulose (London, England)》2009,16(2):167-178
The aim of this work was to investigate the morphological and structural changes associated with mercerization of cellulose
fibres with combined confocal Raman and atomic force microscopy (AFM). During mercerization the alkali induces a change in
polymorphic lattice from cellulose I to II. This was observed by confocal Raman spectroscopy from cellulose samples treated
with 10, 15 and 25% aqueous sodium hydroxide solution. AFM images from the same samples illustrated that microfibrils were
swollen and more granular in cellulose II than in cellulose I. Raman spectral images in plane and depth directions showed
that the polymorphous cellulose structure was uniform throughout the cell wall, whereas the microfibril orientation varied
between fibre cell wall layers. The changes in microfibril orientation on the sample surfaces were confirmed by AFM images
measured from the same sample position. 相似文献